function LogOutput(target: Function, key: string, descriptor: any) {
	console.log(target);//指向类 Car
	console.log(key);//指向函数名 add,descriptor.value 则指向该函数
	console.log(descriptor);//应该是指向 add 函数的描述符{configurable: true,enumerable: true,writable: true,value:fn}

}

class Car {
	length: number = 20;
	@LogOutput
	add (num: number) {
		return num * 2;
	}
}

let c1 = new Car();
c1.add(11);